My questions are: 1) Should a in line attenuator be considered when using a passive pre?No not a great idea unless you know your I/O impedances are still good, as they will change depending (where you put them) the input or output impedance matching, always for the worse, than what you had without them when using your passive preamp..
The best resistance value for a passive preamp is series/shunt 10kohm.
This value is high enough input impedance to suit 99% of sources (except high impedance >2kohm tube output sources)
And low enough to suit most poweramps inputs that are 33k or higher.
Cheers George